The specific aims fo this study are to determine the effects of grapefruit juice on oral cyclosporine pharmacokinetics (clearance) and pharmacodynamics (toxicities) in stable pediatric renal transplant patients. Patients will receive 2 different dosage forms of oral cyclosporine: Sandimmune or Neoral. Serial blook and urine samples will be collected at baseline (cyclosporine alone) and after cyclosporine is administered with grapefruit juice (4-8 ounces three times a day with meals). Differences in pharmacokinetic parameters (volume of distribuition, half-life, and clearance) between cyclosporine alone (Sandimune or Neoral) and cyclosporine with grapefruit juice will be assessed.